Physiological response to drought in seedlings of Pistacia lentiscus (mastic tree)

Drought is often an important constraint on plant regeneration in the Mediterranean. Pistacia lentiscus is of particular interest in restoration actions in fire-prone areas. This study addressed the current knowledge gap on the physiological response of this species to drought during its initial development. We hypothesized that the seedlings would have a high resistance to drought. In addition, we expected that seedlings from two sources with contrasting climate conditions would perform distinctly under drought. Seeds were collected from two populations in north and south Portugal. Seedlings were subjected to a progressively lower osmotic potential during 25 days, through increasing PEG concentration in the hydroponic solution. The physiological response of the seedlings was assessed by measuring gas exchange and chlorophyll fluorescence after 15 and 25 days of drought exposure, when the osmotic potential was −2.47 and −5.17 MPa, respectively. Shoot growth, net CO<inf>2</inf> assimilation rate, stomatal conductance and transpiration were significantly reduced under drought conditions, whilst intrinsic water-use efficiency (IWUE) remained unaffected. This response partially agreed with the known strategy of P. lentiscus to cope with drought, typically maintaining high IWUE, however the observed reduction in stomatal conductance was not as pronounced as expected. Drought induced a decrease in leaf pigments that could be linked to photo-protective mechanisms. Seed source did not have a significant effect on drought response. P. lentiscus showed a high resistance to drought, which clearly supported its use in restoration actions in the Mediterranean, but these findings require further testing under field conditions.